sinc.m

FS1016源代码

% MATLAB SIMULATION OF NSA FS-1016 CELP v3.2
% COPYRIGHT (C) 1995-99 ANDREAS SPANIAS AND TED PAINTER
%
% This Copyright applies only to this particular MATLAB implementation
% of the FS-1016 CELP coder.  The MATLAB software is intended only for educational
% purposes.  No other use is intended or authorized.  This is not a public
% domain program and distribution to individuals or networks is strictly
% prohibited.  Be aware that use of the standard in any form is goverened
% by rules of the US DoD.  Therefore patents and royalties may apply to
% authors, companies, or committees associated with this standard, FS-1016.  For
% questions regarding the MATLAB implementation please contact Andreas
% Spanias at [phone].  For questions on rules,
% royalties, or patents associated with the standard, please contact the DoD.
%
% ALL DERIVATIVE WORKS MUST INCLUDE THIS COPYRIGHT NOTICE.
%
% ******************************************************************
% SINC
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 7-5-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Evaluate the sinc function
%
% DESIGN NOTES
%
% sinc(x) = sin( pi * x ) / ( pi * x )
%
% VARIABLES
%
% INPUTS
%   arg        -     Point(s) at which to evaluate sinc(x)
%
% OUTPUTS
%   s          -     Value(s) of the sinc function
%
% INTERNALS
%   nulls      -     Locations of 0s in the input vector
%   nullcnt    -     Number of 0s in the input vector
%
% ******************************************************************

function s = sinc( arg )

% FIND ZEROS IN THE INPUT VECTOR
nulls = find( arg == 0 );
nullcnt = size( nulls );

% EVALUATE SINC AT ALL POINTS
s = sin(pi*arg) ./ (pi*arg);

% REPLACE NANs WITH 1.0 FOR POINTS EVALUATED AT THE ORIGIN
if nullcnt ~= 0
    s( nulls ) = ones( nullcnt );
end

% RETURN A COLUMN VECTOR
s = s';